Geologic Time Scale Page
Precambrian time begin 4.6 bya it started with the formation of the earth and moon and ended with jellyfish. Bacteria dominated Precambrian time
Paleozoic Era- 540 MYA jawed fish started it and winged insects ended it. Amphibians were most dominant.
Mesozoic Era- 248 MYA age of dinosaurs started it and dinosaurs extinction ended it. Dinosaurs were most dominant during this time
Cenozoic Era- 65 mya eohippus started it and it is contuining on today humans were most dominant during this time
From largest to smallest it is eons, era, period,epochs they are the times and that the earth has been in and it has times inside of times if you understand that we live in the Phanerozoic eon Cenozoic era quaternary period and the Holocene epoch.